Polymeric roof sheeting is used as single ply roofing membrane for covering industrial and commercial flat roofs. Such membranes are generally applied to the roof surface in vulcanized or cured state. Because of outstanding weathering resistance and flexibility, cured EPDM based roof sheeting has been rapidly gaining acceptance. However, a disadvantage of cured rubber roofing is that it requires the use of adhesive for joining and sealing the edges of membranes due to the lack of adhesion of rubber to itself.
Over the years, Thermoplastic Polyolefin (TPO) has been widely used as heat seamable roof sheeting material. It eliminates the use of adhesive to provide an acceptable seam. However, conventional polypropylene based TPO roofing sheets are rather stiff, i.e. not flexible, which is disadvantageous for installation of such membranes in extreme cold weather.
Polyethylene having lower glass transition temperature than polypropylene provides enhanced flexibility, particularly in low temperature would be desirable roofing material to meet cold temperature installation requirement.
One critical requirement to be taken into account when selecting a heat seamable TPO resin is its long-term heat seam peel strength. A conventional Ziegler-Natta catalyzed polyolefin have a bimodal or broad molecular weight distribution. The low molecular weight oligomers extract out of polymer over time. The high extractables of Z-N catalyzed polyolefins are undesirable for heat seamable roofing materials because they bloom to the surface of the sheet and deteriorates the heat seam strength.
Accordingly, it is an object of the present invention to provide a new and improved single ply heat seamable TPO roofing sheets having advantageous low temperature flexibility and heat seam peel strengths.
Another object herein is to provide such roofing sheets in which its membranes have a 90° peel strength of ≧60 lbs/linear inch (ASTM D-413), and a cold brittleness point of ≦−50° C. (ASTM D-2137), over an extended period of use, and under a wide range of temperature conditions.
These and other objects and features herein will be made apparent from the following description of the invention.